Effects of soil and water properties on anionic polyacrylamide sorption

Knowing the sorptive behavior of anionic polyacrylamide (PAM) by soils is useful in predicting the appropriate application rate, depth of effective treatment, and its mobility in soils. Sorption isotherms of PAM by Soil materials, six natural soils, and their subsamples with partial organic matter (OM) removed by H2O2 oxidization under different dissolved salt concentrations were examined. The PAM sorption isotherms can be well described by the Langmuir equation. Soil texture, OM content, and dissolved salts (a combined contribution of soil salinity and irrigation water quality) influenced the extent of PAM sorption. Soils with high clay or silt content and low OM content had a high sorptive affinity, for anionic PAM. The amount of PAM saturation sorption increased significantly as the total dissolved salts (TDS) increased. Divalent cations Ca2+ and Mg2+ were about 28 times more effective in enhancing PAM sorption than monovalent cations Na+ and K+, mainly because of their stronger charge screening ability. The effectiveness of cation enhancement on PAM sorption varied with soil texture and was greater in fine soils than in sandy soils. Organic matter had a negative effect on PAM sorption. Soil samples after the removal of partial OM adsorbed more PAM than natural soils. The negative effect of OM on PAM sorption was attributed to the reduction of accessible sorption sites by cementing inorganic soil components to form aggregates and to the enhancement of electrostatic repulsion between PAM and soil surface by its negatively charged functional groups.